Chemical vapor reaction is an increasingly useful method of processing integrated circuits. There are several classes of such reactions, which are carried out variously at atmospheric or lower pressures, at relatively higher or relatively lower temperatures, and under plasma enhanced or unenhanced condition. While the equipment of this invention has great versatility, it is primarily intended for lower pressure operation at medium to high temperatures.
Because of the high cost of materials used in integrated circuits, it is essential to maintain as high as possible the efficiency and correctness of the processing. It is economically disastrous to scrap high percentages of production runs, especially when they are carried out in batches and when the event causing the scrappage occurs at a later stage of the processing of the material, after many processes have already been completed.
One of the principal causes of scrappage is variation of uniformity in thickness and in resistivity. This in turn is often a function of improper distribution of pressure drops, or of division of flow. Often the imperfect wafers are "streaked". In pyrolytic deposition processes, temperature and time are firstorder effects. Much scrappage is also caused by irregularity in velocity of flow across the wafer because of the effect of velocity on the boundary layer conditions, and on the concentration of the reactants.
Also, in many prior art processes, it is common practice for a reactant stream to flow along a plurality of wafers, one after another. This forms a long reaction path, and the reactant concentration at a downstream wafer varies because of consumption of reactant by an upstream wafer. Furthermore, because many vapor deposition processes are carried out in batch-loading apparatus, it is important to have a large a load capacity per batch as possible. Apparatus in which the wafers are laid side-by-side inherently are spatially inefficient.
It is an object of this invention to provide a chemical vapor reaction system in which there is a short reaction path, an improved uniformity of product, and a high loading efficiency.
A chemical vapor reaction system according to this invention includes a closed reaction vessel which defines a reaction chamber. An end closure member can be opened to give access to the chamber. At least one reactant supply conduit and at least one exhaust port, are provided. These discharge into and exhaust from opposite sides of a reaction region. A boat which holds the workpieces to be treated is disposed in the reaction region. The substrates are held in a "stack" or "stacks", parallel to and spaced from one another so that reactant material flows over their surfaces. They are arranged so that each portion of the reactant stream flows over the surface of only one substrate. A distributor upstream from the substrates distributes reactant to the reaction region.
A reactant supply region and an exhaust region are formed respectively upstream and downstream from the reaction region.
According to a preferred but optional feature, a second distributor is provided downstream from the boat, between the reaction region and the exhaust region.